Clinical signs and symptoms are an essential aspect of the diagnosis of Lyme borreliosis. Thus, a thorough knowledge of the clinical features of the disease is important. Established clinical definitions could be of help in everyday clinical practice and especially to compare the findings of different authors or groups. The characteristic sign that permits the diagnosis of Lyme borreliosis is a typical erythema migrans skin lesion. Highly suggestive manifestations are ear lobe lymphocytoma, acrodermatitis chronica atrophicans and Bannwarth's syndrome. The majority of other signs and symptoms are only suggestive and, when expressed individually, may have a very limited or even symbolic value for the purpose of diagnosis. Laboratory confirmation of borrelial infection is needed, as a rule, for all manifestations of Lyme borreliosis with the exception of typical erythema migrans. In clinical practice indirect laboratory methods are usually employed. Determination of borrelial IgM and IgG antibodies by immunofluorescence assays or enzyme-linked immunosorbent assays has not been standardised, and correlation of the results from different laboratories and/or different commercial tests may be poor. Immunoblotting may solve some of the many dilemmas but could (especially in Europe) raise additional questions in a field in which numerous uncertainties already exist. The reliability of methods for direct detection of borrelial infection other than culture to ascertain spirochetes in tissue specimens is open to question. Treatment with antibiotics is reasonable in all stages of Lyme borreliosis and for all clinical manifestations; however, it has been most effective early in the course of the illness. The choice of antibiotic depends upon many factors including the efficacy, pharmacokinetic profile, side effects, expected compliance and price. For the majority of manifestations the most effective antibiotic, the optimal dosage, and the most appropriate duration of treatment have not been exactly determined. Recommendations for the treatment of Lyme borreliosis in Slovenia are presented.